Some say that Grayscale doesn't own any Bitcoin but that is for debate because they are Investment Trust, and their clients are buyers who own bitcoins.
It's not really much of a debate. Grayscale has cryptocurrencies under its AUM ~ Assets Under Management, this refers to the sum of an asset which a company holds on behalf of it's clients, so Grayscale is sort of like a channel through which investors access cryptocurrencies.
Assets in holding would refer to total assets which the company invested in using company's funds and this would be reflected in their balance sheets. So microstrategy is risking about $450 million in Bitcoin, while Grayscale is not really risking anything.